This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A240765 #20 Aug 06 2020 00:37:47 %S A240765 5,13,6277,26777,27299,40031,44773,194119 %N A240765 Numbers n such that (43^n - 1)/42 is prime. %C A240765 a(8) > 10^5. - _Robert Price_, Apr 12 2014 %H A240765 H. Dubner, <a href="http://dx.doi.org/10.1090/S0025-5718-1993-1185243-9">Generalized repunit primes</a>, Math. Comp., 61 (1993), 927-930. %H A240765 H. Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a> %p A240765 A240765:=n->`if`(isprime((43^n - 1)/42), n, NULL); seq(A240765(n), n=1..100000); # _Wesley Ivan Hurt_, Apr 12 2014 %t A240765 Select[Prime[Range[100000]], PrimeQ[(43^#-1)/42]&] %o A240765 (PARI) is(n)=ispseudoprime((43^n-1)/42) \\ _Charles R Greathouse IV_, Feb 20 2017 %Y A240765 Cf. A028491, A004061, A004062, A004063, A004023, A005808, A004064, A016054, A006032, A006033, A006034, A006035, A127995, A127996, A127997, A127998, A127999, A098438, A128002, A128003, A128004, A128005. %K A240765 hard,more,nonn %O A240765 1,1 %A A240765 _Robert Price_, Apr 12 2014 %E A240765 a(8) from _Paul Bourdelais_, Aug 04 2020